The invention relates to an installation for manufacturing cement clinker from raw meal which is treated thermally in a combustion process by preheating, calcining, sintering and cooling, and the exhaust gas stream of the sintering stage (rotary tubular kiln) and exhaust gas stream (tertiary air) of the cooling stage (clinker cooler) in the calcining stage which is supplied with fuel is used to calcine the raw meal, a combustion chamber with secondary fuel introduced into the upper side of the chamber and a tertiary partial airstream with sub-stoichiometric fuel combustion being integrated in the calcining stage in order to form a CO-containing reduction zone for reducing the pollutant NOx, and the underside of the combustion chamber being connected via a connecting line to the lower region of the rotary kiln exhaust gas rising line. Furthermore, the invention relates to a method for operating such an installation.
Installations for manufacturing cement clinker from raw meal of the type described above which have a calcining stage which is connected upstream of the rotary tubular kiln and is double fired have to be capable of producing raw meal which is calcinated to a high degree before introduction into the rotary tubular kiln. At the same time, the manufacturers and operators of cement clinker production lines are faced with the problem of using secondary fuels and with increasingly stringent requirements for low emission values for pollutants such as NOx and CO.
In order to reduce such emissions of pollutants it is known to integrate into the calcining stage in a cement clinker production installation (specialist publication “World Cement” February 1995, article on pages 2 to 8, in particular FIGS. 1 and 7) what is referred to as an RSP calcining combustion chamber through which there is a flow from top to bottom and in the upper side of which a calcining fuel, a first tertiary partial airstream and raw meal which is preheated from the second lowest cyclone stage of the raw meal preheater, and tangentially below it a second tertiary partial airstream is blown in and causes the parties to the reaction in the combustion chamber to swirl. In the combustion chamber, the fuels are burnt sub-stoichiometrically, that is to say with a deficit of oxygen, in order to form a CO-containing reduction zone in order to reduce the pollutant NOx which has been formed in particular as a result of the high temperature burning in the rotary tubular kiln (thermal NOx). For this purpose, the underside of the RSP combustion chamber is connected via a connecting line to the lower region of the rotary kiln exhaust gas rising line so that in the known cement clinker production line the CO-containing reduction zone extends from the interior of the calcining combustion chamber via the lower connecting line into the rotary kiln exhaust gas rising line and there up to the 180° tubular line manifold of the rotary kiln exhaust gas rising line because it is only there where a third tertiary partial airstream is introduced in order to burn off, by means of excess oxygen, any residue of the non-consumed CO which has remained in the entire long NOx reduction zone.
In the known cement clinker production line with the RSP calcining combustion chamber, the length of the CO-containing reduction zone cannot be readily adapted to the NOx content which is present in the rotary kiln exhaust gas and has to be reduced and/or to the type, pellet size and property of the secondary fuels used in the calcining combustion chamber.